Logitext is an educational proof assistant for first-order classical
logic using the sequent calculus, in the same tradition as Jape, Pandora, Panda and Yoda.
It is intended to assist students who are learning Gentzen trees
as a way of structuring derivations of logical statements.
Underneath the hood, Logitext interfaces with Coq in order to check
the validity of your proof steps. The frontend is written in
Haskell and Ur/Web, and there is an
interesting story behind it which you can read about. Alternatively, get the source at
GitHub.

To get started, check out the tutorial, or dive right
in and type in something to prove: